Deep-well drilling tools having parts which are movable for longitudinal displacement in relation to one another require a moving contact sealing means between the parts, which prevents penetration of drilling fluid into an interior annular chamber of the tool, filled with oil, for example. The differential pressure occurring at such sealing means depends not only on the pressure drop of the drilling fluid on its way from the inner circulation compartment of the drilling string through the further tools disposed below the tool parts which are longitudinally displaceable into the annular space of the well but also on the dynamic pressure of the oil in the inner annular chamber which builds up because of the delay in equalization of the volume of oil through narrow equalization passages on longitudinal displacement of the parts. The differential pressure may additionally depend on the size of tool, the viscosity of the oil as well as the temperature and may reach values of up to 1000 bar.
Results from the field use of deep-well drilling tools show that defects appearing at the high-pressure sealing means between the parts which are movable for longitudinal displacement must be regarded as the main cause of the premature failure of these tools. Accordingly, numerous attempts have been made to use in deep-well drilling moving contact sealing means of the most varied configuration and nature of material, which have proved satisfactory in other fields of application. Field trials using such sealing means did not, however, lead to an increase in service life.
It is therefore an object of the present invention to provide a high-pressure sealing means for parts which are movable for displacement in relation to one another, which achieves a service life corresponding to the life of conventional drilling tools, under field conditions in deep-well drilling tools, making special allowance for the marginal conditions which occur here.